Control system for aerial photography



s. P. wlLLlTs ETAL 3,158,079

8 Sheets-Sheet 1 Nov. 24, 1964 CONTROL SYSTEM FOR AERIAL PHOTOGRAPHYOriginal Filed March 28, 1957 Nov. 24, 1964 s. P. wlLLlTs ETAT.3,158,079

CONTROL SYSTEM FOR AERIAL PHOTOGRAPHY 8 sheets-sheet 2 Original FiledMarch zal, 1957 MANUAL COMPUTER )0) Q Illl l f i? o 55a MII OPTlCAl. nSCANNER 52 1- 7 @5U-TT SCANNER CONVERTER 5313556 55 52 -l /55`57 SCANNERl5; MANUAL CENTRAL "26 COMPUTER E X470 @SRV/27 1,5

sTATloN T129 COMPUTER 64 l 7 62 65 6667 mmm 69 A l IIIIIIHIN llllll( '760 69 l IM] 7, 5.9 +D.C.

75 PoTENTloMETER S'GNAL GROUND 72' H 73 79 [In] 70 7:9-A 74 1lu1|||||||l||| VELOCITY SCALE |||||1IN|| Hl-ALT.

E 0R soE R R 86 I /fvl/EA/oRs:

` @45% ATTORWM Nov. 24, 1964 s. P.w1| LxTs ETAL CONTROL SYSTEM FoaAERIAL PHOTOGRAPHY Original Filed March 28, 1957 8 Sheets-Sheet 3 Wmd)www Mmmm/iw www Nov. 24, 1964 s. P. wlLLlTs ETAL 3,158,079

CONTROL SYSTEM FOR AERIAL PHOTOGRAPHY Original Filed March 28, 1957 8Sheets-Sheet 4 f7 f W9 h fall A SYNCHRO TRANSMITTER de/lfd w @y A? of? lNov. 24, 1964 s. P. wlLLlTs ETAL. 3,153,079

CONTROL SYSTEM FOR AERIAL PHOTOGRAPHY Original Filed March 28, 195'? 8Sheets-Shea?I 5 Nov. 24, `1964 s. P. wlLLlTs ETAL. 3,158,079

CONTROL SYSTEM FOR AERIAL PHOTOGRAPHY Original Filed March 28, 1957 8Sheets-Sheet 6 MN/W@ W4@ @pm/?. WMe/n S. P. WILLITS ETAL CONTROL SYSTEMFOR AERIAL PHOTDGRAPHY Original Filed March 28, 1957 8 Sheets-Sheet '7OTHER SOLENOIDS J klllll T /Nl/ENTORS:

j www Nov. 24, 1964 s. P. wlLLlTs ETAL 3,158,079

CONTROL SYSTEM Foa AERIAL PHOTOGRAPHY Original Filed March 28, 1957 8Sheets-Sheet 8 W .ZZ @g3 wi-acm' BF is? 414/ 68 \B\Bco United StatesPatent O 3,158,d79 CNTRQL SYSTEM EUR AERIAL PHOTOGRAPHY Samuel l.Willits, Barrington, and William L. Mohan,

Prospect Heights, lll., assignors to Chicago Aerial Industries, line.,llarrington, Ill., a corporation of Delaware @riginal application Mar.28, 1957, Ser. No. 649,078, now Patent No. Zo'Wtl, dated Jan. l0, 196i.Divided and this application dan. 9, wl, Ser. No. 81,440

l2 Claims. (Cl. 95-12.5)

rl`his invention relates generally to a control system for erial camerasand more particularly to a new and improved control system for one ormore serial cameras in which the picture taking rate and motion impartedto film or camera is controlled to compensate for image motion at thephotographic plane. This application is a division of the co-pendingapplication of Samuel P. Willits, William L. Mohan, and ames M. McCarty,tiled March 28, 1957, Serial No. 649,078, now Patent No. 2,967,470.

One of the basic requirements of an aerial camera control system is thatit produces negatives of high resolution. One of the features whichreduces photographic resolution is image motion. It is known that theeffect of image motion may be offset by supplying a compensatory motionto the lilm or to the camera during exposure.

in view of the increasing capability for speed in prescnt day aircraft,the need for more accurate means to decrease the blurring effectproduced by the relative ob- ;ect motion during photographic exposurehas become more significant. In the prior art, this compensation hasusually been made by rotating the aerial camera at a rate such that thecamera optical axes remain aligned with a fixed point on the objectplane during exposure or, alternatively, by moving the hlm in the Cameraat a rate such that a point on the film remains aligned with a fixedpoint on the object plane during exposure.

These techniques, which frequently are referred to as image motioncompensation or IMC, generally have proven satisfactory since it hasbeen found that the change of the distance or angular position usuallyis of secondary importance. Such compensatory motion may be defined bythe following equation.

11:1.689 Fsine 0 (l) where also is frequently required that an aerialphotographic system be capable of taking pictures at discrete periodicintervals. it may further be necessary that sequential frames orpictures have a predetermined amount of overlap. rl`his overlap7 usuallyexpressed as a percentage, is useful in providing stereoscopic viewingof the resultant prints and also in mapping for the purpose of keying aseries of photographs together. For maximum usefulness the overlap mustbe maintained with good precision to avoid changing the trigonometricrelationships used in preparing a topographic map. By way of example,the accuracy required by the military services varies between plus orminus and plus o1' minus 3%. As reduced to practice in the presentinvention, these limts are substantially bettered.

ICC

It will readily be understood by those skilled in the art that theoverlap of successive exposures is dependent on the time intervalbetween exposures or the rate at which exposures are made per unit oftime. An equation which may be used to determine the picture taking ratefor any value of overlap from 0 to 100% is:

For the purpose of the description which follows it should be noted thatin Equations l and 2 above, velocity (V) and altitude (H) of theaircraft are the only variables subject to change during ilight. Theseelements are ldesignated as iti-flight variables. The remainingelcrnents of Equations 1 and 2 are known before the flight and hence aredesignated as pre-flight variables.

Several control systems for aerial photography which provide for thecontrol of the picture taking rate and image motion compensation areknown but the degree of accuracy attained by such prior art systems hasnot proved entirely satisfactory. For the control of IMC, the majorityof prior art systems have means for providing an electrical potentialproportional to aircraft velocity and altitude. This potential then isfed into an electronic computer in combination with the datacorresponding to the pre-flight variables to provide an output voltageproportional to all of the variables. This output voltage then isapplied to a conventional velocity servo mechanism to control the speedof the film drive motor or the velocity of a camera mount.

The accuracy of systems of the type just described is dependent upon anumber of independent variables. These include the accuracy with whichthe velocity to altitude ratio V/H is determined and maintained, thedegree of precision with which this ratio is converted to an electricalpotential, the accuracy of the electronic computer that integrates thepre-liight variables into the computation and linally, the ability ofthe velocity servo mechanism to translate the computed output potentialinto the desired velocity.

Further, a variety of systems have hitherto been devised to control thepicture taking interval. One of the most common of these is a manuallyset timing device which uses a constant speed drive mechanism to controla switch initiated camera operation. Devices of this type normally arereferred to as intervalometers and although they generally are accurate,they also are cumbersome to utilize since they require laboriouscalculations on the part of the operator. They also have theVdisadvantage that when either of the in-llight variables is changed,the calculations must be repeated and reentered into the intervalometer.This obviously is unsatisfactory under conditions such as militaryreconnaissance Where evasive action often must be taken during aphotographic run.

It has no-t hitherto been known how to devise an aerial photographiccontrol system which is capable of providing image motion compensationand control of the picture taking rate with the precision required forpresent day aircraft. More simply, prior to this invention there has notbeen available aerial camera control mechanisms having they accuracyrequired for reducing the factors de- 3 tracting from photographicresolution to only the camera optical system, the lilm characteristics,and iiight turbulence.

Accordingly, it is a primary object of this invention to provide a newcontrol system for aerial photography which is characterized by itsimproved accuracy of image motion compensation and its control of thepicture taking rate.

lt is a more specic object of this invention to provide an improvedaerial photographic control system capable of precisely measuringaircraft angular velocity and accurately converting this informationinto compensatory film velocity and picture taking rate control.

It is still another object of this invention to provide such an improvedaerial photographic control system in which the entry and computation ofpre-flight variables is greatly simplified and which is capable ofautomatically adjusting to changes in the in-ilight variables.

It is a further object of this invention to provide an improved controlsystem for aerial photography which perg mits continuous monitoring ofthe source of information of in-iiight data.

It is still another object of this invention to provide such a controlsystem having means for substantially eliminating any computation forthe manual entry of the in-liight data when it is not available from anautomatically operating source.

Still another object of this invention is the provision of means forsynchronizing the operation of a camera with a mechanical shaft rotationin a more precise manner than was heretofore possible.

It is another object of this invention to provide a control system foraerial photography adapted to control several different types of cameraswithout requiring modification of the cameras. More particularly, it isan object of this invention to provide an improved camera control systemfor image motion compensation and picture taking interval control whichis not limited as to iilm format dimensions, film transport mechanismand camera focal length.

It is a still further object of this inventon to provide an improvedsystem capable of synchronizing the exposures of a plurality of cameraswhich have their respective optical axes at various angles of depressionrelative to the horizontal.

Still another object of this invention is the provision of an improvedaerial camera control system capable of operating several cameras in apredetermined repetitive sequence.

Still another object of this invention is the provision of a systemcapable of selective action in accordance with the camera focal axisdepression angle below the horizontal wherein image motion compensationand picture taking rate is readjusted to the correct value correspondingto this angle each time the angle is changed.

in accordance with a specific illustrative embodiment of the inventionthese and other objects are attained in a novel aerial camera controlsystem which employs mechanical analogue principles whereby the aircraftangular velocity data V/H is converted to a D.C. potential and thispotential then is translated into a corresponding mechanical shaftrotation. Calculations of the picture taking rate and TMC then areeffected by a gear ratio changing means to the end that integrationofthe pre-flight variables is accomplished with substantially zeroerror. This results in a substantial increase in accuracy over aerialphotographic control systems now in use.

A feature of the invention is the use of a rotary synchronoustransmitter driven in accordance with the shaft rotation to control thefilm velocity by means of a positional servo mechanism. Thus, in oneaspect of this invention, precise control of film velocity is achievedby utilizing a positional servo mechanism as a velocity control device.This unique arrangement is very effective for even though a positionalservo mechanism is subject i to certain positional errors with respectto the rotary synchronous transmitteer, its angular velocity erroressentially is zero.

In another feature of the invention, the rotary synchronous transmitterdriven by the shaft rotation in accordance with the angular velocitydata V/ H is used to control the rocking motion of a swinging or IMCcamera mount. Thus, the camera in the mount is rocked in an arc at anangular rate corresponding to the V/H data.

Accurate measurement of the aircraft angular velocity and the correctionof errors which may result both in the determination of the aircraftangular velocity data and the conversion of this data to compensatingiilm Velocity and picture taking interval control information isachieved through the use of an optical view finder which cooperates witha servo mechanism to the end that the compensatory film velocity andpicture taking interval control information is present in the viewfinder field of view as moving grid lines. In accordance with thisinvention these moving grid lines move in synchronism with the terrainonly when the determination and conversion of aircraft angular velocityis correct.

Still another feature of this invention is the provision of a variablespeed transmission in combination with a servo mechanism, a rotarysynchronous transmitter and cam operated switches to providecompensatory lm velocity control and control of the picture takinginterval for various cameras in accordance with camera focal length, lmformat size, focal axis and depression angle below the horizontal. Oneaspect of the invention is that the rotary synchronous transmitter andthe cam operated switches are utilized to provide compensatory filmvelocity control and control of picture taking rate, respectively.

Still another feature of this invention is the provision of image motioncompensation Without restriction as to camera film transport mechanism,lens focal length, or film format size by means of a positional servomechanism which is adapted to cooperate with a pivotable mount and amount actuating device to the end that the entire camera assembly isrocked at a compensatory angular velocity.

During the course of an aerial photographic flight, it frequently isnecessary to obtain photographs at velocity to altitude ratios whichexceed the limitations of a single camera as for example, where thepicture taking interval becomes less than the camera recycle time. Suchlimitations are circumvented in accordance with a feature of thisinvention by a novel arrangement for operating a plurality of cameras ina predetermined repetitive sequence. This result is realized in oneillustrative embodiment by the use of cam operated switches, incombination with a variable speed transmission and velocity servomechanism, as pulse rate dividers and distributors. These act todistribute the basic single camera exposure initiating pulses among twoor more channels whose exposure initiating pulse rates then become l/Ntimes the basic rate where N is the number of cameras to be operated inthe repetitive sequence.

Still another feature of the invention is the synchronization of theexposures of several cameras through the use of positional servomechanisms whereby the shutters of the several cameras are trippedsimultaneously.

The above and other features of novelty which characterize thisinvention are pointed out with particularity in the claims annexed toand forming a part of this speciiication. For a better understanding ofthis invention, however, and its advantages reference is had to theaccompanying drawings and descriptive matter in which is illustrated anddescribed several specific illustrative ernbodiments of the invention.

ln the drawings:

FGURE 1 is a block diagram illustration of an aerial camera controlsystem embodying features of this invention;

FIGURE 2 is a schematic block diagram representation of the inventionillustrating the manual computer or automatic scanner control of thecentral computer;

FIGURE 3 is a diagrammatic illustration showing in greater detail theconstruction of the manual computer;

FIGURES 4, 5, 6, 7 and 8 illustrate the construction of the range gearchanging mechanism;

FIGURE 9 shows the construction of illustrative station computer;

FIGURE l is a simplified schematic diagram illustrating the connectionof two pulse cameras for either simultaneous or alternate sequentialoperation;

FlGURE l1 is a simplied schematic and block diagram illustrating theconnection of an autocycle camera to the camera control system of theinvention;

FIGURES l2, 13 and 14 are waveform diagrams illustrating the operationof the circuits of FlGURES 11 and l;

FGURE l5 is a schematic diagram of a servo amplifier embodying theinvention;

EGURE 16 is a simplified schematic and block diagram illustrating thecontrol system connections for the simultaneous operation of two pulselll/IC cameras;

FIGURE 17 is a simplified schematic and blocl: diagram showing a pulselll/IC camera connected for day or night operation;

FlC-URES 18 and 19 illustrate the operation of a pulse camera in anlll/1C camera mount when connected with a camera control system inaccordance with the invention;

FlGUlrE 20 illustrates the operation of the camera control system with acamera in a rotatable mount but not provided with an llt/1C mountactuator;

FGURE 21 is a schematic and block diagram of an alternate stationcomputer and pulse distribution system for pulse operated cameras;

FGURE 22 illustrates a switch of the type which may be used with thestation computer' of the present invention;

FIGURE 23 shows in detail the construction of cmbodimcnt of stationcomputer which may be utilized in thc system of FlGURE 2l;

FlGURE 24 is a simplied schematic of the electrical portion of thestation computer shown in FlGURES 21 and 23; and

FlGURES 25, 26, 27 and 28 illustrate the principles of the view nder, asshown in FGURE 2.

Referring now to the drawing and more particularly to FlGURE 1, there isshown in block diagram form an illustrative aerial camera control systemwhich is representative of the general principles of the invention. Thesystem comprises an optical scanner, designated by the reference numerallil, which advantageously may serve as one source of iii-flight variabledata, namely velocity, V, and altitude above the terrain, l-i. Opticalscanner lil may take any suitable form and advantageously may be shownin the patent to D. Hancock, lr. and H. E. Meinema, 2,413,349, issuedDecember 31, 1946. ln operation, scanner lil originates an electricalsignal proportional to the velocity to altitude ratio, hereinafterreferred to as V/H. rlhe scannei signal is applied to a scannerconverter lll where it is converted to a DC. signal, designated as ER,having an amplitude proportional to the scanner signal. Advantageously,scanner converter l1 may be constructed as disclosed in theabove-identified Hancock and Meinema patent.

The DC. voltage output LR of scanner converter lll is applied to amanual computer l2 which also serves as a manually operable alternatesource of l//H information in a manner further described below. A switchon manual computer l2 enables the operator to choose between the manualcomputer l2 and the optical scanner l@ as the source of V/,H informationfor the camera control system. From manual computer i12, the D C. signalER is transmitted to a central computer designated generally at 1d.

Central computer lll comprises a velocity servo system camera recycletime.

l5, a gear changing mechanism le, a line shaft l' coupled to the gearchanging mechanism 16 and a synchro transmitter 18 together with aplurality of individual station computer units 19, Ztl, 2l and 22, eachhaving a station computer Z9 coupled to line shaft 17.

ln accordance with a feature of this invention, the DC. voltage ER isconverted to a mechanical shaft rotation in the central computer lit. Aswill become apparent from the more detailed description givenhereinbelow, calculations of the picture taking rate and lMC are made byunique gear ratio changing means to the end that the integration of thepre-flight variables into the computation is accomplished withsubstantially zero error. This results in a substantial increase inaccuracy over die prior art aerial photographic control systemsheretofore utilized.

The conversion of the ER voltage to a shaft rotation is effected in thevelocity servo system 15 by the DC. generator 23, the servo motor Z4 andthe amplilier 25 which rresponds to the ER voltage to vary the speed ofmotor 24 in accordance with the amplitude of the ER control sgnal. Motor24 has its shaft coupled to the range rear changing mechanism 16 whichtransmits the motor shaft velocity at a ratio of 1:1 or 1:10 inaccordance with a control signal received over conductor 27 from eitherthe scanner converter 11 or the manual computer 12.

Coupled to the output of the range gear changing mechanism 16 is a lineshaft 1.7 which in turn is coupled to a synchro transmitter 118. Theoutput of synchro transmitter 18, as applied over conductor 2S to thecontrol system, is a rotational data reference signal which is afunction of V/H. A plurality of individual station computer units suchas units 19, Ztl, 21 and 22, also are coupled to the line shaft 17, asby means of suitable bevel gears and the like.

Each of the station computer units comprises a station computer 29 inthe form of a gear changing unit which is adapted to provide a pluralityof changeable gear ratios to permit computation for desired overlap,focal length, format size and depression angle, otherwise known as thepre-flight variables. The rotational output of each station computer 29serves to drive the rotor of a synchro transmitter 3@ at a speedcorresponding to the computed camera cycling rate to thereby provide arotational lMC reference voltage for one or more cooperating cameras ata given camera station. rl`he output of each station computer 29 alsodrives pulse switching cam means 31 to provide one or more switchclosures for pulsing a single camera or camera array, or two or morekcameras operating sequentially. Thus, each station computer Z9 iscapable of supplying both IMC and pulse information to a camera station.

At camera station 1 in FIGURE 1 there are shown two pulse type cameras32 and 33 connected for sequential operation. A pulse camera, as thename implies, operates on the basis of pulsed control signals.` When apulse is received by the camera it actuates the camera shutter whichthen initiates its own signal to command film winding and rewinding ofthe shutter if necessary. As cameras of this type operate with a singlepulse governing the picture taking rate, itis necessary that the timeseparation of sequential pulses be `greater than the When the pulseseparation is less than the carnera'recycle time it is necessary to usemore than one camera and to distribute the control pulses betweencameras.`

In the two pulse camera system shown at station l', the stationcomputeroutput speed is decreased by suitable gearing to one-half of itsnormal speed and the two pulsefswitches are provided apart., Each camerais connected to one switch, as for example, camera 32 to switch 3ft, andcamera 33 to switch 35. ln this manner each pulse to a camera occurs atthe time it would occur yif there had been no gear reduction to the cam31 operating-the switches and each camera then is operated at atesoraone-half of the picture taking rate. It will be appreciated that a gearreduction to one-fourth speed for the cam and four switches wouldprovide for sequential operation of four cameras, and, similarly, a gearreduction to one-third speed and three switches would provide forsequential operation of three cameras. Further, a single camera orsingle camera array may be operated from a station computer having twoor more switches and having the switch operating cam appropriatelyreduced in speed merely by connecting all of the switches together, asillustrated at camera stations 3 and 4 in FIGURE l.

Camera station 2 comprises an autocycle camera 36 with its associatedservo amplier 3'7. Autocycle cameras, or camera magazines, arecontrolled by an EMC command signal. This command signal controls ilmspeed in that the lilm holding platen and/or the tilm is moved at IMCspeed and the camera or magazine originates a shutter tripping pulsewhile the lilm is moving at this speed. The film is then advanced,normally at a faster rate than IMC speed, to supply fresh tilm to theexposure area, after which IMC speed is resumed, the shutter tripped,and the cycle repeated. Cameras of this type provide an overlap ofsequential exposure based only on camera design.

Similar to the autocycle cameras with reference only to the controlsignal required are strip cameras. The IMC command signal controls thespeed of the filrn to synchronize it with the image of the ground as theiilm moves continuously past an open slit.

The illustrative autocycle camera 3-5 shown at camera station 2 inFIGURE 1 is adapted to be used in an azimuth mount 3d which corrects thealignment of the camera to compensate for aircraft drift. Asillustrated, the autocycle camera 36 receives the IMC command signalfrom the synchro transmitter in station computer unit 2l through servoamplitier 37 and azimuth mount 38 receives the dritt alignment signalfrom the viewlinder Sti.

A tri-camera array comprising cameras 39, 4th and 41, having similarparameters `as described above, is shown at camera station 3 connectedto be pulsed from the paralleled pulse switches at station computer unit20. Manifestly, such an arrangement is desirable since the pre-nightdata is identical for cameras 39, it? and 41.

Camera station Il in FIGURE l comprises a swinging or IMC mount l2 whichsupports a pulse camera 43. The IMC mount t2 together with its servoamplitier i4 achieves image motion compensation by rocking camera in anarc at an angular rate corresponding to the velocity to altitude ratioV/H. As shown, the camera i3 receives its control pulses from theparalleled pulse switches in station computer unit 19, and the IMC mount42 and servo amplifier t4 receive the V/H data from the synchrotransmitter l in the central computer.

While the four camera stations shown in FIGURE 1 illustrate fourdifferent camera configurations which advantageously may be used withthe novel camera control system of the invention, it will be understoodby those skilled in the art that advantageously numerous other cameraconfigurations may be used therewith with equally successful results.For example, all of the camera stations could he provided with pulse IMCcameras for a night reconnaissance flight. In such an application thecamera shutter is opened and the tilm is moved continuously in thecamera at a speed determined by an IMC command signal. Pulses ifrom astation computer release a dare cartridge or bomb at intervals inaccordance with the desired picture taking rate. The explosion of theliare cartridge or bomb originates a second pulse from a hare detectorwhich closes the shutter and causes the tlm to recycle after which theshutter reopens. The next computer pulse repeats the sequence, etc.Cameras of this type may be used sequentially in the same manner aspulse cameras.

Day operation orc pulse IMC carreras differs principally from nightoperation in that the computer pulse operates Cit o GD

a conventional shutter in place of releasing a flare cartridge or bomb.After shutter closure, the lilm is ad- Vanced and the tilm velocityreturns to the IMC rate until the next shutter operating control pulse.By this method it is possible to vary the overlap of sequentialexposures as contrasted with autocycle cameras Where this is notpossible.

The aerial camera control system shown in FIGURE l also comprises aplurality of station control units 45, d6, l? and itl whichadvantageously may include oir-oit switches for supplying power tocamera stations l, 2, 3 and respectively. In accordance with an aspectof this invention the supplying of power to the camera stations as wellas to other system components, such as optical scanner tu, scannerconverter' 2i, etc., does not permit the taking of pictures but merelypermits Warm-up ot these various components. Picture taking commenceswhen an operating switch, which may be located at any convenient placein the aircraft, is closed.

The camera control system shown in FIGURE l also includes a flarecontrol and a viewnder shown generally at tl, which is described ingreater detail below.

As explained heretofore there is more than one possible source for theV/H control data. A preferred arrangement tor the camera control systemof the invention would include both the optical scanner fr@ togetherwith the scanner converter Il and the manual computer Till, although itwill be understood that only one such source is required.

The optical scanner Stil and its converter il function as an automaticsource of i//H control data in accordance with the Hancock and lvleinemapatent identified above. Briefly, the optical scanner l@ originates anelectrical signal which has a frequency proportional to the V/H ratio.The scanner converter il converts this frequency to a DC. voltage ERWhich has an amplitude proportional to this frequency.

The alternative source of I//H information, the manual computer I2, isshown in greater detail in FIGURES 2 and 3 of the drawing. rEhe manualcomputer l2 comprises a double pole, double throw switch Si whichincludes a switch blade operatively associated with a pair of Stationarycontacts 53 and 5f-i, and a switch blade 55 ganged to switch blade 52and operatively associated with a pair of stationary contacts 5d and5'?. Stationary contacts 53 and 56 are connected to the output ofscanner converter il and in the operating position of switch 5l shown inFIGURE 2 the ER control signal from the scanner converter is appliedthrough switch blades and 55 to the central computer Stationary contactsSlt and 57 of switch Si are connected to terminals of switch 8?; in themanual computer potentiometer and in the other operating position ofswitch 5l, the ER control signal is applied from potentiometer 5Sthrough switch blades and S5 to central computer M.

rthe manual computer potentiometer 53 is constructei to permit th-nshaft wth the wiper and the housing to he rotated separately. rI`his isbetter seen in FiGUR-E i which a knob 59 on hollow shaft @d is shownatached to a gear 6l. Hollow shaft dit is rotatably mounted on stud u2and is restrained from axial motion by retainer 63. Advantageously, stud62 may be secured to the support housing 64 in any suitable manner.

Gear dll meshes with gear d5 which is fixed to the potentiometer shaftd. Shaft (s6 is rotatably mounted in bearings 6'7 and 68 which are.fixed to the support housing 6d. An altitude scale 69 is affixed to tothe end that rotation of knob 5*, also rotates potentiometer shaft tidto provide an indication of tie magnitude of rotation by means of thescale o@ and an indicator mark (not shown) attached to the supporthousing 6d.

The velocity scale 'iti and the potentiometer housing 71 are actuated ina similar manner. Knob 72 is attached to hollow shaft 'f3 which in turnis attached to gear Tifl. Hollow shaft 73 is rotatably mounted on stud75 and is Sassone restrained from axial movement by retaining ring 76.Stud 75 is secured to the support housing o4 in any suitable manner.Gear 7d meshes with gear i7 which is rotatably mounted on shaft 78. Avelocity scale "itl is aixed to gear 77 and, by means of studs 79, topotentiometer housing '7 which carries resistance in a manner well knownin the art. lt now will be appreciated that rotation of knob 72 resultsin a rotation of potentiometer housing '7l with an indication `of themagnitude of rotation given by velocity scale 7@ and an indicator mark(not shown) attached to the support housing It can be seen from theschematic diagram of EIG- URE 2 that the potentiometer wiper hl isconnected through switch blade 52 of switch tif) to contact Sri ofswitch 5l. Potentiometer wiper 8l is positioned in slidn ing contactwith the logarithmetic resistance element Si) which is connected to asource of potential tid. Thus, when Switch l is in the MANUAL position,i.e., with switch blade S2 connected to Contact and switch blade 55connected to contact 57, a potential ER deri ed from the potentiometerEll and the source of potential is supplied to the central computer lig.Conversely, when switch 5l in the SCANNER position, ie., with switchblade 52 connected to contact 53 and switch blade 555 connected tocontact L'o, the ER potential is supplied by the optical scanner l@ andthe scanner converter lll. Accordingly, it will be appreciated thatswitch 5l enables the operator to select the source of ER voltage fromeither the automatic scanner system or the potentiometer means Of themanual computer'.

It is manifest that the ratio of l//H decreases with creasing altitudewith a resulting decrease in the ER volt age. As the ER voltagedecreases, the control vcltcgcs supplied to the servo motor 245- alsodecrease with the result that any errors increase proportionally inmagnitude. ln accordance with an aspect of this invention, thisundesirable result is avoided by an automatic switching circuit in boththe scanner converter ll and the manual computer l2 whereby the ERvoltage is increased by a factor of l0 whenever it falls below a firstpredetermined level. Control signals thus raised by a factor o ll0 aretermed High Altitude signals. Similarly, the ER voltage is decreased bythe factor of l) whenever the control signal returns to a secondpredetermined level. Advarn tageously two separate levels are providedfor control of the automatic switching circuit. A single predeterminedlevel could be used for this purpose, but this is not preerred due tothe possib ity of repeated switching taking place for aircraft operationat or near this single level. This possibility is obviated by theprovision of separated iirst and second predetermined levels. As the ERvoltage supplied to the amplier 25' in the central computer ld controlsthe speed of the servo motor 2d, the speed of the latter is increased ordecreased by the factor of l0 with this change in voltage.

Additionally, a reduction gear train in the range ge r changingmechanism llo is actuated by remotely controlled means whenever the HighAltitude; signal is present. rThis gear reduction is engaged to reduceoutput rotational speed by the same factor of 10 for High Altitudesignals and is disengaged whenever the control signals are not in theHigh Altitude range. Thus, changes in the speed of servo motor M due toswitching to a higher or lower Voltage range are cancelled out and theservo system is operated within a speed range where inaccuracies areheld to a minimum.

One .illustrative means for accomplishing switching between HighAltitude and normal ER ranges is in the manual computer as shown inFlGURES 2 and 3. The potentiometer i3 of the manual computer l2 has twowipers 8l and S5 placed with respect to each other such that thepotential measured across wiper 35 and potential source 3dis l0 timesthe potential measured across wiper hl and potential sourcell A cambiosecured to shaft 78 of the potentiometer changes the position of.maintain this proportion at ratios other than lzl.

switch blades 32 and 37 of switch 83 in response to changes of thealtitude setting. Thus, at the predetermined altitude level, theposition of switch 83 changes and contact for switch blade S2 istransferred from wiper Sli to wiper 85 or from wiper 535 to wiper At thesaine time, switch blade $7 of switch S3 opens or closes a circuitbetween a source of potential tid and Contact 57 of the SCANNER-MANUALswitch 5l for use when switch 5l is in the lli/[ANUAL position to supplypower to a r agnetic actuating means in the range gear changingmechanism lid. Thus, for the condition where lOER is supplied to theamplifier 25, the gear reduction in range gear changing mechanism i6 isengaged, while for normal values of ER the gear reduction is disengaged.

lt will be appreciated by those skilled in the art that the mechanicalswitch Vmeans for increasing the ER signal lO-fold as escribed above maybe replaced by any other suitable electrical or electronic means capableof attaining the same result and in anot er illustrative ernbodiment itis contemplated that conventional voltage sensitive relays may besubstituted for the switch 83 in the manual computer.

ln accordance with a major feature of the invention, the ER signal datais converted to a shaft rotation having a velocity proportional to theamplitude of the ER signal by the velocity servo system of the centralcomputer indicated generally at l5 in ElGURES l and 2. This servo systemcomprises a conventional arrangement of an amplifier 2S connected` atits output to a DAC. servo motor and at its input to a DE. generator`23.Motor 2li and generator 23 share a common armature shaft 9i) which alsois coupled to the range gear changer ld.

The positive ER control signal from switch blade 52 of theSCANNER-MANUAL switch 51 is connected to the positive terminal of DC.generator Z3 and the negative terminal of the generator 2? is connectedto the input of amplilier 25. In this manner the difference between theER signal and the output voltage of generator Z3 forms the input to theamplier 25.

When servo motor 2d is operating at a speed less than that required bythe ER signal, the output voltage of generator 23 is less than the ERsignal and a positive difference voltage is supplied to the amplifier25. Ampliiier 25 has a current output which is proportional to thediilerence voltage applied to its input and for positive dittcrencevoltages the current output increases with increases in the voltageinput.

The current output of amplii'ier 25 is applied to the armature of servomotor Zd and as the current output increases, the motor speed and hencethe generator speed tends to increase. As generator speed increases thegenerator voltage increases to thereby reduce the difference voltagebetween the generator output and the ER- command signal. This processcontinues until the dicerence voltage is reduced to Zero at which timemotor 24 is operating at the speed required by the ER signal.

lt will be understood by those skilled in the art that when the servomotor is operating at a higher speed than that reguired by the signal,the outputoi generator 23 is greater than the ER signal and a negativedifei'ence volt e is applied to ampliiier Z5. Amplifier 25 thendecreases its current output to the armature of servo motor 2d the motoris slowed down until it is operating at the speed required by the ERsignal.

Accordingly, in the manner explained above, the output shaft of servomotor 2d is caused to rotate at a speed proportional lto the V/H ratio,as controlled by the ER signal. Consideration of the operatingcharacteristics of the servo motor and of gear ratios necessary in thestation computer. 29 indicates that it is desirable to A preferred ratioand one actually used in an embodiment of this invention 'sets the servomotor output speed at either 5.63 l//hy revolutions per second or 56.3l//H p Lne atesora l l revolutions per second. As will become apparentfrom the description given hereinbelovv, the output speed of the centralcomputer line shaft 17, to which the station computers 29 are coupled,is maintained at a constant value of 5.63 V/H revolutions per second.

The coupling of the output shaft @l of servo motor 2d to the range gearchanging mechanism lo is shown in greater detail in FIGURES 4, 5, 6, 7and 8 of the drawing. The range gear changing mechanism is a form oftransmission with a preferred velocity ratio from input to output ofeither 1:1 or 1:l0, as desired. lvianifestly, other ratios may beemployed in lieu of these preferred ratios With equally7 advantageousresults.

As shown in FlGURE 4 the output shaft @l of servo motor Z4 is rotatablymounted in bearings @E and 93 which, in turn, are secued in any suitablemanner to the supporting structure Gears 95 and llo are secured to shaft@1, as for example, by threaded split hubs (not shown) attached to thegears together with nuts Advantageously, retaining rings may bepositioned in annular grooves provided in shaft ill to maintain theshaft, and hence gears l5 and 9d, in a desired axial position.

The output shaft l', which is the central computer line shaft, of therange gear changing mechanism Ito is rotatably mounted in bearings andlll@ which, in turn, are secured to the supporting structure lill.Retaining rings lll@ are positioned in annular grooves in shaft l? tomaintain the shaft, and hence gears ltl and lud, in position axially.Gear lila is rotatably mounted on line shaft i7 so as to mesh with gearGear 1 is restrained from axial movement by retaining rings l set inannular grooves in line shaft l'. Gear also is rotatably mounted on lineshaft 31.7 and is in mesh with gear 95. Gear SZ is restrained from ardalmovement by retaining rings loe set in annular grooves of line shaft i7.

ln the illustrated embodi nent, gears and i454 are identical and hencehave a velocity ratio of lzl. Gear 95 advantageously is smaller thangear lti and in this embodiment the gears have a velocity ratio of 1:10.ln accordance with an aspect of this invention, either gea or gear idfmay he operatively coupled to lin shaft l? for rotating the latter bythe gear shifter coupling generally indicated at "o7 in FEGURE 4 andillustrated in greater detail in FlGS. 5, 6, 7 and 8.

ln FlGURE 5, the gear shifteicoupling lill is shown in the position forproviding a 1:1 velocity ratio mission from input shaft @i to outputline shaf coupling has a body idf), fhich advantageously may be anintegral enlarged diameter' of line shaft 1 body ltl is provided with anannular' groove El? and a radial hole llt? to provide clearance for a s;ring lll. This is shown in greater detail in FlGURE S wh can be seenthat the shape of spring ill to maintain the spring i position in grooveonce it is pressed into this pcs ion. A formed central portion lllZ ofspring lll tends to keep the spring in the position shown in 5. A notchlili at one edge of central portion 112 of the spring lll operativelyengages an annular groove lla in driving pin Driving pin 11rd isassembled through two aligned holes in body lili; in such a manner thatit has rotational dom and is limited in axial movement by the centralportion il?. of spring lll.

A. selector pin llo is positioned in an axial clearance hole in lineshaft 17 and advantageously is made of sufficient length of contact thecentral portion ll of spring lll at one end of the pin and to extendbeyond the end of line shaft i7 at the other end of the pin. lt can beseen that if selector pin lid is moved to the right from the positionshown in FlGUlE 5 it would overcome the spring force exerted by thecentral portion 1132 of spring and cause the central portion of thespring to assume the position illustrated in FIGURE 6.

lt will be noted that as the spring central portion 1l?. is moved to theright, it causes the driving pin 1l5 to move to the right along with it.

@ne preferred method for actuating the selector pin ll is by theenergization of the solenoid M7 shown in FEGURE 4. When the solenoid isenergized, its armature llt; is placed into contact with selector pin115 to move the selector pin to the right from the position shown inFGURE 4 of the drawing. lt is now understood that this results indriving pin llS also being moved to the right With respect to itsillustrated posiion in FlGURE 4.

When the solenoid ll is cle-energized, the coupling is in the normalposition illustrated in FIGURE 4. ln this position drivin pin llS isheld by the pressure of the U central portion i12 in a position where itwill intercept longitudinally a pin lll@ secured to gear 134 uponrotation of this gear. When the input shaft 9i is rotated by servo motor24, gear and its meshing also are rotated. This causes pin il@ on gearEN to engage driving pin M5 and the resulting rotary force istransferred to coupling body 1% to rotate line shaft l? at a speedidentical to that of shaft 9i. lt will be appreciated that as the servomotor driving shaft 9i. is constrained by its method of connection tosingle direction of rotation, bacli lash is of no consequence.

vl/'hen the solenoid lll? is energized by the High Altitude signal overconductor 27 from the manual computer 12 or the scanner converter ll, asdescribed above, selector pin lil-5 and hence driving pin 15 are movedto the position shown in FlGURE 6. ln this position, driving 1in llfidoes not intercept pin llllJ on gear l'ii but the driving pin doesintercept pin 12d secured to gear ltl. When the servo motor output shaft@l and gears 95 and ltl are rotated, pin l2@ on gear M3 interceptsdriving pin J5' on the coupling M7. Conscquently, coupling M57 and henceline shaft i7 are rotated at a speed 1A() of that of shaft @l because ofthe reduction interposed oy gears 95 and lil.

Referring now to FlGURE l of the drawing, it can he seen that line shaft17 extends a considerable distance from the range gear change mechanismlo to drive several add. nal components. Additionally, it now isunderstood that line shaft f7 is rotated a speed proportional to theV/I-lv ratio in accordance with signals supplied by either t'ne opticalscanner 1li or the manual computer l2.. As shown in FIGURES l and 2, asynchro transmitter lo of conventional design is coupled to the lineshaft if? such as by gear lZl secured to the line shaft and its meshinggear lZZ coupled to synchro transmitter It. As explained in greaterdetail below, synchro transmitter 1d is utilized to supply to the systema rotational data reference potential which is a function of the l//Hinformation.

A plurality of station computers 29, such as those shown at computerstation units i9, Ell, 231 and 22 are detachably coupled to line shaftll at spaced intervals along the length of the line shaft. As shown inFIG- URE 2, each station computer' 29 is preferably coupled to lineshaft i7 by means of a pair of miter gears H3 and gear 123 is secured toline shaft 17 and gear irq-.4 is secured to stub shaf' Advantageously,each station comnuter 2%? is detachably coupled to its stub shaft 1225by means of a male coupling 112s secured to the stub shaft which isadapted to engage a female coupling :127 secured to the input shaft ofthe station computer rlfne male cou-.plint7 and the female coupling 127are keyed to fit together in only a single predetermined fashion for35u" of rotation to the end that the phase relation therebetv een beconstant, as explained further below.

The principal features of the construction of a station com uter 29 areshown in FlGURE. 9 of the drawing. lnput rotational motion to thestation computer Z9 is eiected by female coupling 127 secured to one endof th-e station computer input shaft Shaft 12b is rotatably journaied ina bearing 129 and carries at its other end miter gear 136. Miter gear136 is in mesh with miter gear 131 which is secured to the stationcomputer drive shaft 132. Shaft 132 has affixed thereon a gear 133 inmesh with gear 135 and a gear 134 in mesh with gear 135, each of thegears 135 and 135 being carried by shaft 137.

A plurality of other shafts and gears are provided in station computer129 and like shafts 132. and 137; each of these shafts is rotatablymounted in suitable bearings provided in frames 133 and 139.

rl`able l below describes the relation of the various gears and variousshafts in the station computers and preferable gear ratios which obtainbetween various numbers of the gears:

TABLE I Moshcs With Shaft Gears Preferred No. Gear On Shaft Gear Ratio-so as to rotate therewith. Further, it will be understood that eachshaft having a gear shifter coupling thereon is hollow to provideclearance for the coupling selector pin 116, as described above.

Advantageously, a manuallyoperated push button or 14 remotely controlledoperating means such as a solenoid, or both, is associated with theselector pins of each of the gear shifter couplings 167. Where only asolenoid is provided to eiiect the gear changing through a gear shiftercoupling, a solenoid such as that schematically indicated at 175 inFEGURE 9 may be secured to a supporting structure by suitable fasteningmeans (not shown) so that the solenoid plunger 176 is aligned with theselector pin 1552 of coupling 167 on shaft 137. Thus, when solenoid 175is energized its plunger 175 is actuated to move selector pin 152 to theright from the position shown in FIGURE y9 to effect a change in theposition of the driving pin of the gear shifter and hence to change theoperating gear ratio between shaft 132 and 137.

Still another preferred embodiment of a switching solenoid to effectgear changing is shown in FIGURE 9 by the solenoid indicated at 177.When the solenoid 177 is energized its plunger 17d contacts bell crank179 which is pivotally mounted on pin 166. The bell crank 179 pivotscounterclockwise on pin 156 to depress selector pin 181 on shaft 142.One advantageous feature of this arrangement is that a push button, suchas that indicated at B, also may be used to pivot the bell crank 179.

It will be understood that each of the gear Shifters in the stationcomputer may be operated by either a solenoid of the types describedabove or a push button, such as those indicated at A, B, C, D, E and Ffor shafts 137, 142, 149, 154, 159 and 166, respectively, or by both asolenoid and a push button, if desired.

It is contemplated that the push buttons and the solenoids are of thetype which remain in their actuated positions until they are released.Suitable push buttons and solenoids adopted for this purpose are knownto those skilled in the art.

Now it can be appreciated that in accordance with the novel features ofthis invention, operator set up of the various gear ratios necessary forintegration of the predight variables into the station computercomputation can easily and quickly be eiected by means of the buttonand/or solenoid associated with each of the gear shifter couplings. Thecooperation between the shifter couplings, the selector pins and thepush buttons, together with the gear ratios obtained for each selectorpin in its operated or released condition, are given in the followingtable.

TABLE II Sllier Associated Preferred Gear Ratio Dciilgiiaiion ShaftSelector Shifter Shifter Pin Depressed Released 1t will be appreciatedthat the total station computer gear ratio for the illustrative stationcomputer embodiment shown in FIGURE 9 is the product of the six in-'ividual gear shifter ratios. Further, it will be appreciated that theoverall gear ratio of the station computer may be varied as desired toobtain various picture taking rates. To determine the gear ratio, GRrequired for a specified picture taking rate, R, in pictures per second,the following equation may be used:

` RH r,

Where the'variables H and V have the same meanings describedhereinabove. fj

15 A preferred method that may be used to obtain station computer gearratio, where the overlap and the other pre-flight variables have beenspecied, is by the use of a chart wherein the gear ratios for the morecom- L1 Lil@ more or less than two switches may be used with cam 174,provided the gear reduction between the switch operating cam shaft 173and the station .computer output is changed accordingly. It will furtherbe understood monly used values of pre-flight variables have been pre- 5that the number of couplings and the numerical value of computed. Thisserves to substantially simplify the optheir various corresponding gearratios given in the above erators task, for all he need do is refer tothe chart and description of a station computer can be changed inacdepress the combination of push buttons indicated therecordance withthe requirements placed on the control syson. For example, theembodiment of station computer tem, and that the foregoing descriptionof a station comillustrated in FlGURE 9 of the drawings advantageously10 puter with six gear shifter couplings and the various gear may haveassociated therewith an instruction plate conratios indicated in TableII are merely illustrative of the taining the information tabulated inTable lll below for invention. indicating the proper combinations ofpush buttons A, B, Referring now to FIGURE l there are shown two C, D, Eand F to be depressed for predetermined sets of pulse cameras 177 and173, which are connected for pre-night variables: l either simultaneousor alternate sequential operation. A

TABLE nr Focal Length 2% 1% s e 12 Forma'cFlight Direction 9 6 12 24 as4s Optical Asis Overlap Percent Push In Buttons 2o 57 ec so 90 90 None nBCD BC BDF BF 9U BE BCE BDEF BEF BCPEF BCEF g so 15 B Bo BDF BF BCDF BOF4.5 BD BoD Bo BDF BF BCDF gai 3o 15 None o DF F CDF oF Q 5 ACD DE NoneBDE B BGDE 5 Dn BDE B BODE Bo BDEF Referring again to FIGURE 9, it canbe seen that the station computer, generally indicated at 179, has asuitsynchro transmitter 3d advantageously may have its rotor able gearreduction from its output driving shaft 173 with driven at the samespeed as the output of the station its attached cam 171ito alternatelyeect closure of the computer. rEhe phase relationship of the synchrotranstwo switches generally indicated at 1S@ and 131. A mitter output isestablished with respect to a xed posisource o potential 152, which hasits negative terminal tion of the input coupling 127 and hence the lineshaft 17 45 connected to ground, has its positive terminal connected ofthe centr computer. At this position the electrical to the switch blades133 and 13d of switches 1S@ and zero or" the synchro transmitter 3d isset. Positive ioca- S1, respectively. The stationary contact 185 ofswitch tion of the electrical zero of the synchro transmitter 3i? 131 isconnected to pulse camera 17d and the stationary with respect to thecoupling 127 is made by the design of contact 156 of switch 18@ isconnected to pulse camera the gear shifter couplings 167 wherein drivingContact be- 50 177. ln actual practice, suitable pulse shaping circuitstween a gear and the coupling is effected in only one having a pulseoutput of constant duration regardless oi position rior each revolutionof the gear. As a result, the pulse separation would be provided betweenthe switches electrical zero and the phase relationship of the synchroand the pulse cameras, but for the purpose of simplifying transmittersin the different station computers can he the explanation of the switchoperation, these pulse shapmade substantially identical for a given lineshaft angular ing circuits have not been shown. position it the shiftersettings in the different station comit can now be seen that with noconnection between puters are the same. the conductors leading to pulsecameras 177 and 17d, a The output of the synchro transmitter 3d thusprovides pulse resulting from the closure of switch 181 actuates arotational MC reference potential for one or more copulse camera 173 andsimilarly, after 180 of rotation ot operating cameras at a given camerastation. A cam 17dl 6() cam 174, a pulse resulting from the closure ofswitch secured to shaft 173 is rotated at one halt the speed of the 13Gactuates pulse camera 177. It can readily be seen station computeroutput by means of the reduction efthat if the conductors to the twopulse cameras are confected by gear 171 on the synchro transmitter shaft17th nected together, as by ya conductor 137 shown dotted in and gear172 on shatt 173. A pair of pulse switches 175 FlGURE l0, closure ofeither switch 181B or 131 will and 176 are operatively associated withcam 171tand are G5 actuate both cameras. Further, if only one camera ispositioned with respect to cam 174 to be alternately used, the inclusionof conductor 187 would result in that closed thereby, i.e., one switchof the pair is closed for camera receiving pulses at the computed rate.Manifesteach 180 of cam rotation. Further, switches 175 and ly,inclusion oi the connecting conductor 107 can be made 176 are locatedwith respect to a iixed position of the either permanently or by a relayoperated from some reinput coupling 127 in a manner similar to thatdescribed 70 mote location. above for the synchro transmitters 3i) tothe end that like FGURE 1l is a simplified schematic diagram whichswitches of different station computers are closed at subshows ingreater detail than in FIGURE. 1 the connection stantially the identicalinstant in time if the shifter settings of an autocycle camera 3o to thecontrol system o the in the diiterent stations are the same. invention.The gear train of the station computer 29 It will be understood by thoseSkilled in the art that drives the rotor 15S of synchro transmitter 3i)at a speed atesora 1 7 proportional to the camera cycling rate. Rotor1%3 receives power from a transformer 139 in the servo amplifier 37 bymeans of conductor 217. As the rotor 138 is rotated, varying voltagesare impressed on the several stator windings 19d in a manner well knownin the art.

A synchro receiver 191 located in the autocycle camera 3d has its statorwindings 192 connected to the stator windings 190 of the synchrotransmitter E@ in the station computer. The rotor 193 of the synchroreceiver 191 is driven by the film drive motor 194 through -a gear box195. The synchro receiver rotor 193 has two windings 196 and 197positioned 90 apart electrically. To facilitate the followingexplanation of the operation of the autocycle camera, rotor winding 197will be designated as camera B winding and rotor winding 196 will bedesignated as camera A winding. The camera B winding 197 is in phasewith the rotor 18? of the synchro transmitter ftl when the camera drivemotor is rotating at the correct speed, and for Zero phase relation theoutput from the camera B winding 197 will be at a maximum. rI`he outputof the camera A rotor winding 196 will be low under these conditions.Since the film drive mechanism 1% is driven by the ylrn drive motor 19dsimultaneously with the rotor `192', of the synchro receiver 1571, foran iti-phase relationship between the rotors of the synchro transmitterSi) and the synchro receiver 191, the film will be moved at the IMCvelocity.

Here another of the features of this invention becomes apparent. The twosynchros in combination with the lm drive motor 12d and the servoamplifier 37 comprise a positional servo mechanism utilized as avelocity control device. The importance of this feature is evident whenit is recalled that although a positional servo mechanism is subject tocertain positional errors with respect to the synchro transmitter, itsvelocity error is substantially zero.

Since the power supplied to the rotor 138 of the synchro transmitterfit1 by transformer 129 advantageously is derived from the aircraftpower system, the frequency of its output will be that of the aircraftpower system, a frequency which commonly is 40() cycles per second. As aresult, the output of the camera synchro rotor 193 is a 400 cycle signalwhich is modulated at a frequency dependent on the speed differencebetween the two synehros. For example, if the relative motion betweenthe two synchros is 60 rpm., then the modulation frequency is 1 cycleper second.

An illustrative example of the waveform of lthe camera synchro outputwhen a speed difference exists is shown in FIG. 12. When the camera isrunning at synchronous speed, but out of the phase, the output is thatof the waveform shown in FIGURE 13. it will be noted from FIG- URE 13that both output conductors from the synchro receiver rotor windings 196and 197 have. a signal amplitude proportional to the 400 cycle supplyfrequency, but no modulating frequency.

The outputs of the camera A winding 1% and the camera B winding 197 ofthe synchro receiver rotor 193 are applied to separate demodulationcircuits in the servo amplifier 37. Camera B winding output is appliedto demodulator 199, and camera A winding output is applied todernodulator 2110. The demodulator outputs are shown in lFIGURE 14 ofthe dnawings. Direction arrow 2&1 in FIGURE 14 indicates waveprogression for increasing time when the receiver synchro rotor 193 isunderspeed and where signal A leads signal ld. Direction `arrow 2112 inFIGURE 14 indicates wave progression for increasing time for theoverspeed case where signal B leads signal A. 1t will be under-stood bythose skilled in the art that phase reversal occurs whenever a camerasynchro operating underspeed begins to operate overspeed or vice versa.

The outputs of demodulators 199 and 2li@ are applied to a logicalcomputer 2&3 which serves to detect if camera A signal or camera Bsignal is leading. in addition, the camera A conductor from demodulator2% applies an error signal to a voltage amplifier 29d which controls theoutput of a magnetic amplifier 2115. Although amplifiers 204- and 205may be constructed in accordance with voltage and magnetic amplifierswell known .to those versed in the electronic arts, 4an illustrativeconstruction for these amplifiers is shown in the schematic circuit ofFIGURE 15. The magnetic amplifier 265 controls the armature current ofdrive motor 191i in the camera to complete the servo loopt.

Whenever a speed difference exists between the transmitter synchro Si)andthe camera drive motor, the logical computer 2113 functions. Foroverspeed, the power supply from logical computer 223 to the magneticamplifier 295 by way of conductor 2do is opened. Por underspeed, a verylarge (in comparison `to the A error signal) error signal is added fromlogical computer 2113 to the input of amplifier 204 by Way of conductor2M. This signal, occasionally referred to as a slugging signal, resultsin a relatively large output from amplifier 2h41 and causes maximumpower output of magnetic amplifier 205. When the motor 124 and synchroreceiver 1% are at the command speed, the computer 2u?) maintains powerto the magnetic amplier, but does not slug amplifier 294. In this case,only the A error signal is present at the input of amplifier 2114, andit controls the two amplifiers to correct for any small difference inphase angle existing between the two synchro rotors 19@ and 193.

An illustrative embodiment of servo amplifier 37 is shown in schematicform in FIGURE. 15 of the drawings. When the system master vori-oliswitch and the station power are on, DC. power is supplied to the servoamplier over conductor 21) and 40() cycle A.C. power is supplied to theservo amplifier over conductors 211 and 212. Conductor 212 is connectedto prim-ary winding 213 and the A C. voltage thereon energizestransformer 189. Secondary winding 215 of transformer 139 suppliesheater power to the various electron tubes. Winding 216 suppliesexcitation by conductor 217 to the rotor 183 of the synchro transmitter19t) in the station computer. Winding 214 supplies the AC. voltage inputfor full wave rectifier 213 which comprises a bridge arrangement ofdiodes 219, 221i, 221 and 222. Rectifier 213 is connected at its outputto a filter comprising choke 244i and capacitor 245 and serves as theDC. voltage supply over conductor 268 for the anodes of electron tubes224, 225 and 22o in servo amplifier 37.

The modulated signals from camera A winding 1% and camera B winding 197of synchro receiver rotor 193 are applied to separate windings 227 and228, respectively, on transformer 189. The camera B signals aredemodulated in the circuit consisting of resistor 229, diodes 230 and231, resistor 232 and capacitor 233. The camera A signals aredemodulated in the circuit consisting of resistor 234, diodes 235 `and236, resistor 237 and capacitor 23d. Advantageously, the resistors ineach demodulator circuit are maintained substantially equal so that thevoltage amplitude at the input will equal the voltage amplitude at theoutput.

rIhe demodulated camera B output from demodulator 199 is applied to thegrid Mil of tube 2261A through bias resistor 239. The demodulated cameraA output from demo-dulator 209 is applied to the grid 243 of tube 224Bthrough bias resistor 241, and through bias resistor 242 to the input ofa conventional voltage amplifier generally indicated at 204 andcomprising tubes 225 and 226. The anode current of tube 224A controlsthe coil 247 of relay R2 connected between the anode 246 and the DC.voltage supply. The anode current of tube 224B controls the coil 241i ofrelay R1 connected between anode 249 and the DC. voltage supply. RelaysR1 and R2 together' with relays R3 and Rd, constitute a computer whichserves to detect if the camera A or B demodulated signal is leading andhence, whether the camera is operating overspeed or underspeed.

Tables 1V and V, which summarize the relay conditions atesora i@ for thevarious phase angles of demodulator output, are set out below tofacilitate the description of computer operation. Table IV correspondsto the direction arrow 221i in the phase diagram of FIGURE 14, and TableV corresponds to the direction arrow 222.

TABLE IV.-UNDERSPEED Relay Signal Sigral Amplifier 204 R1 R2 R3 R40-1r/2 N N E N Proportional Control. 7r/2-1r E N E N D0. 1r-31r/2 -l- EE E E slugging 31,-/2-21r N E E E Do. 27.*-51r/2 N N E E D0. 51r/2-31r-l- E N E N Proportional Control. 31o-71112 -i- -l- E E E E Slugging.71r/2-41r -I- N E E E Do. 41r-91r/2 N N E E D0.

Ne-Not Enorgized; E-Encrgizcd.

TABLE v.-ovnns1 nnn Relay 0 Sig/rial Siglnal Amplifier 204- Rl R2 R3 R491r/2-41r N N E E slugging. 4rr71r/2 -l- N E E E DO. 71r/2-31r -i- E E EE Do. 31.--51r/2 E N E N Proportional Control` 51r/2-2n' N N E N DO.21r-31r/2 N E N N Cut Off. aqr/z-W E n n: N D0. Iwwf/2 E N N N Do.lr-/2-0 N N E N Proportional Control.

N-Not Energizcd; E-Enorgized.

When the camera is operating underspeed and the station operate switch256 is closed, the following conditions obtain. Closing of the operateswitch 25d completes a circuit from ground through diode 251, resistor252, coil 253 of relay R3, normally closed contacts 254 of relay R2,normally closed contacts 255 of relay Rl and conductor 229 to D.C.voltage source 256. Operate switch 25@ also completes a circuit fromground through diode 257 and resistor 25S to the cathodes 259 and 26@ oftube 224. Assuming for convenience that the operate switch is closed att=0 in FIGURE 14, the following occurs during the first quarter cycle,or from phase angle zero t0 1r/ 2.

During this period, both of the camera A and camera B error signals arenegative so that neither half of tube 224.'- conducts and relays Rl andR2 are not energized. D.C. voltage from source 256 is applied overconductor 2l@ through the normally closed contacts 255 of relay Rl, andthe normally closed contacts 254 of relay R2 to coil 253 of relay R3which is then energized. Relay R3 when energized closes its normallyopen contacts 261, 262 and 263, respectively. This establishes a new DC,voltage path to maintain coil 253 of relay R3 energized through itscontacts 262. Also, contacts 263 of relay RS are closed to apply 490cycles A.C. voltage from conductor 221 to the magnetic amplifier 205.

During this period, with the camera A error signal negative, the outputof amplifier 2M signals the control windings of magnetic amplifier 255to decrease the speed of the camera servo motor i9@ in a manneranalogous to, but the reverse of, that described below for the nextquarter cycle. Current flow through the magnetic amplifier 205 isreduced to that required for magnetizing and, since this is far lessthan that required by the motor 291i to start, it remains stopped.

During the second quarter cycle or from 1r/2 to 1r, the camera A signalis positive and the camera B signal negative. Tube 224B then conducts toenergize coil 248 .2@ of relay Rl. Relay R1 operates to open itsnormally closed contacts 255 and to close its normally open contacts264. This transfers the D.C. voltage from source 256 from contacts 255to 264 of relay Rl from whence it is applied through the normally closedcontacts 265 of relay R2 and through resistor 266 to ground. Relay R3,and hence magnetic amplifier 265, remain energized since relay R3continues to be supplied through its now closed contacts 262. Since thecamera A signal is positive, tube 225A of amplifier 2M conducts anddrives the grid of tube 226B more negative. When the grid of tube 226Bgoes negative, tube 226B is cut ofi, and with it the control winding 267of magnetic amplifier 20S that is con nected between the tube D.C.voltage supply conductor 263 and the anode of tube 226B.

As the grid of tube 225A goes positive with the A error signal, itscathode 269 and cathode 276 of tube 225B tend to follow. This develops apositive going potential at the anode of tube 225B and, hence, at thegrid of tube 226A. Tube 226A conducts and current flows from groundthrough resistance 268, tube 226A and the control winding 269 of themagnetic amplifier 205, to the DC. voltage supply conductor 26S. Thiscurrent tlow increases the saturation of the core of the magneticamplifier 2ti5 and current fiows to the full wave bridge rectifier 234comprising diodes 27E, 272, 273 and 274, respectively, which suppliesthe lm drive motor 194 in the camera 36 through conductors 275 and 276.Motor 294 starts, and its speed increases in proportion to the magnitudeof the camera A error signal.

Assuming that camera 36 does not reach the command speed for some timeand phase reversal of the A and B signals does not take piace, then inthe third quarter cycle from 1r to 31e/2, both the camera A and camera Bsignals are positive. As a result, both halves of tube 224 conduct tomaintain the coil 243 of relay R1 energized and, further, to energizethe coil 247 of relay R2. Relay R2 operates to close its normally opencontacts 277 and 278. This completes a DC. voltage circuit through thenow closed contacts 264 of relay Rl, the now closed contacts 278 ofrelay R2, the now closed contacts 261 of relay R3, coil 279 of relay Rl,and resistor 266 to ground.

Thus energized, relay R4 operates to close its normally open contacts230 and 281. Closure of contacts 281 establishes a new DC. voltagecircuit to maintain coil 279 of relay R4 energized. Also, the closure ofcontacts 280 of relay R4 applies the D.C. voltage on conductor 210 tothe input of amplifier 204, i.e., at the grid of tube 225A, through nowclosed contacts 262 of relay R3, coil 253 of relay R3, now closedcontacts 280 of relay R4 and bias resistor 282. This potential is verylarge in comparison to any camera A signal and, hence it is termed aslugging potential. lt is present whenever relay Re is energized.Amplifier 204 responds by applying a large potential diierence to thecontrol windings 267 and of magnetic amplifier This saturates the magfnetic amplifier 265 and the maximum current then ows to the camera drivemotor 1% through magnetic amplirier winding 283, full wave bridgerectifier 234 and oonductors 275 and 276.

During the fourth quarter cycle from 31r/ 2 to 21|-, relay Ril isrie-energized in the manner described heretofore since the camera Asignal is negative. The camera B signal remains positive andconsequently relay R2 remains energized. The D.C. voltage circuitthrough contacts 255 of relay R11 and contacts 277 of: relay R2 isopened at contacts 285 of relay R4. Relays R3 and R4 remain energized sothat not only the applied power but also .slugging of amplifier 2M andmagnetic amplifier 205 continues.

From 21r to 51.-/2 in the fifth quarter cycle, both relays- Ril and R2are de-energized since both the camera A and B signals are negative.Relays R3 and R4 remain energized and full power continues to be appliedto the film drive motor 194.

In the sixth quarter cycle from 51r/2 to 31r, the camera A signal isposit-ive and the camera B signal is negative. Thus, relays R1, R2 andR3 are in the same condition las in the second quarter cycle from vr/ 2to 1r described above. The DC. voltage applied to the ground side ofcoil 279 of relay R4 through now closed contacts 264 of relay R1 andnormally closed contacts 265 of relay R2 causes relay R4 to becometie-energized. This opens its contacts 280 to stop the slugging ofamplifier 204, and proportional control of film drive motor speed 194 bythe camera A signal resumes.

ln the event that the film drive motor 1-24 is not yet up to commandspeed, the following four quarter cycles are ,the same as those in theperiod from fr to 311, etc. As soon as the camera motor 194 operatesoverspeed, a phase reversal of the demodulated camera error signalstakes place and camera B signal leads camera A signal. Assuming that themotor goes overspeed while receiving a slugging voltage to increase itsspeed and that phase reversal of the A and B signals occur at 91r/2 inFIG- URE l4, the chart of Table V, supra, applies together withdirection arrow 292 of `FIGURE 14.

In the first quarter lcycle of FGURE 14 from 911-/2 to 41r in theover-speed direction, both camera A and camera B signals are negative.Hence, relays R1 and R2 are de-energized. Relays R3 and R4 remainenergized and full power continues to be applied to the film drive motor194 to increase its speed.

In the second quarter cycle of overspeed, from 41r t0 71r/2, the cameraA signal is negative `and `the camera B signal positive. Therefore, coil247 of relay R2 is energized vand relay R1 remains de-energized. TheD.C. voltage circuit through relay contacts 255 of rel-ay R1 andcontacts 277 of relay R2 is opened at contacts 285 of relay R4. RelaysR3 and R4 remain energized and full power continues to be applied to thecamera film drive motor 194.

From 71r/ 2 to 31|- in the third quarter cycle, both camera A and cameraB signals are positive, and all four relays R1, R2, R3 and R4 areenergized. Consequently, full power to the motor 194 continues.

ln the fourth quarter cycle of overspeed from 31T to Sar/2, the camera Asignal is positive and the camera B signal is negative, therebyde-energizing relay R2. The

DC. voltageonfconductor 210 .then is applied through contacts 264 ofrelay R1 and contacts 265 of relay R2 to the ,ground side of coil 279 ofrelay R4, thereby deenergizing relay R4. This opens contacts 280 ofrelay R4 to stop the slugging of amplifier 204. Since relay R3 lremainsclosed and the camera A signal is positive, power to the camera filmdrive motor 194 continues and the motor continues to increase in speed.

It should be noted that the example illustrated in FIG. 14 is for theworst possible conditions, i.e., where the motor reaches overspeed andphase reversal occurs at or slightly prior to 51r/2 or 91r/2. Underthese conditions, the motor 194 continues to increase in speed for fourone-quarter cycles of the modulating frequency. While this is notprobable in actual operation, if it does occur, then both the modulatingfrequency and the camera A error signal yincrease as the motor increasesthe error between its speed and the command speed. Hence, the timeperiod consumed in these four quarter cycles is relatively short, and asthe camera A error signal is cornparatively large, the motor will assumethe command speed quickly.

lFrom Sfr/2 lto 27r in the fifth quarter cycle, both camera A and cameraB signals .are negative. Relay R3 remains energized and relays R1, R2and R4 de-energized. vSince-the camera A signal is negative, amplifier204 reverses the current to the control ,windings 267 and 269 ofmagnetic amplifier 265. This decreases the current flow through themagnetic amplifier and the film drive motor 194 is slowed down.

inthe sixth yquarter cycle from 21|- to 3117/2, thegcamera A signal isnegative and the camera B signal is positive. Relays R1 and R4 remaindci-energized, and relay R2 is energized. This establishes a D C.voltage circuit through contacts 255 of relay R1, contacts 277 of relayR2, and contacts 285 of relay R4 to the ground side of coil 253 of relayR3. This de-energizes R3 and opens its contacts 263 which supply A C.voltage to winding 283 of magnetic amplifier 205. With the magneticamplifier 295 cut ofi, all power to the camera film drive motor 124 iscut off and its speed decreases.

Assuming that camera speed continues to be greater than the commandspeed so that phase reversal of the error signals ,does not occur, themagnetic amplifier 2F15 and the motor 194 will remain cut 4off untilboth of the camera A and B signals are negative as in the period from1r/2 to O or 51.-/ 2 to 21r. ln this quarter cycle, relay R3 isenergized and with it the magnetic amplifier 205 as describedhereinabove. Motor speed will continue to decrease yduring this periodsince the camera A error signal is negative, but if phase reversal doestake place, proportional control by the kcamera A error signal continuesin the next quarter cycle, yas for example, the period from 2mto 31T/ 2kof FiGURE 14, and the motor 194 will increase in speed since camera Asignal will be positive.

When the station computer synchro 3d and the camera synchro 191 arerunning at the same speed, there is no modulating frequency output fromthe rotor 193 of the camera synchro. As described hereinabove, for azero phase angle and synchronous speed between the rotors of the twosynchros, the output of the camera B winding 197 is at a maximum and theoutput of the camera A winding 196 is substantially Zero. The outputfrom the demodulators 199 and 20d of the servo amplifier 37 re- .ectsrthis condition. The demodulated camera B signal is at a maximum andnegative while the camera A signal is substantially zero.

For slight errors in phase angle, the demodulated `camera B .output isslightly less negative and the camera A slightly more or less than zero.lf the rotor 193 of the camera synchro 191 leads the rotor 1S@ of thestation computer synchro Btl, the earner-a A demodulated error signal isnegative and hence reduces the power to the camera film drive motor 194tending to drop it into phase. `If the rotor 193 of the camera synchro191 lags behind the rotor 188 of the station computer synchro 3G, thecamera A demodulated error signal is positive and hence increasesamplifier power to the camera film drive motor y1.94 to attempt to bringit into phase.

As described heretofore, autocycle cameras are capable of providingtheir own shutter tripping pulses and are lfurther capable ofcontrolling the overlap of successive pictures as a function of cameradesign. lt will be appreciated by those skilled in the art that becauseshutter trip is not independent of IMC, it is more difcult to providefor `alternate sequential exposures in autocycle canieras than withpulse or pulse IMC cameras.

It is contemplated, however, to provide sequential operation of twoautocycle cameras with the control system of the invention. rl`his isattained by altering the pattern of push'buttons depressed on thestation compu-.ter so that one-half of the desired picture taining rateis present at the station computer output. One autocycle camera land itsassociated servo amplifier then are controlled in the manner describedabove. The second autocycle camera has its stator input shiftedelectrically and is controlled in a similar manner. Both autocyclecarneras in a system of this type would have gear shifting means adaptedto double the speed of the film during the period that it is moving atIMC speed.

The IMC film speed of continuous strip cameras advantageously can becontrolled in the same manner as that described for lautocycle cameras.However, a D.C. generator tachometer may be added to the shaft of thecamera drive motor. The output of this generator tachonieter then isused as a speed reference by an exposure control system to automaticallyvary the width of the camera slit as a function of the film speed.

The system connections for the simultaneous operation of two pulse IMCcameras 300 and 301 is shown in the simplified diagram of FIGURE 16 ofthe drawings. Camera 300 has operatively associated with it a servoamplitier 302 and camera 301 has operatively associated therewith aservo amplifier 333. Each camera and servo amplier combination operateswith respect to film IMC speed in the same manner as describedheretofore for an autocycle camera. Unlike autocycle cameras, however,the pulse IMC camera does not originate its shutter tripping pulse butrather it depends upon an outside source for such pulses.

In FIGURE 16, the IMC film speed of the two cameras 300 and 301 iscontrolled by the synchro transmitter 3i) in station computer unit andthe shutter controlling pulses originate in station computer unit 19 atthe switches 304 :and 30S therein. It will be understood that by thusseparating the command sources for IMC film speed and shutter trip of =apulse IMC camera, it is possible to vary the overlap of successivephotographs.

When the operate switch 306 is closed, a connection is provided betweenground `and the switch blades of the two pulse switches 304 and 305.Also, a ground connection is provided for the camera servo amplifiers302 and 303. The film in each camera is moved at IMC speed until one ofthe two pulse switches 304 and 305 is closed by the action of cam 174.This operates the shutters or" both cameras which then signal theirrespective lm drive mechanisms to advance, at high speed, a fresh supplyof film to the exposure area. After the lm is advanced, the IMC speed isresumed until the next shutter operation.

A pulse IMC camera connected for day or night operation is showndiagrammatically in FIGURE 17 of the drawings. Camera 307 and itsassociated servo amplifier 303 are operated in an identical manner ineither the day or night mode with respect to the film IMC speed underthe control of the synchro transmitter 30 in the station computer. Thisoperation is the same as that described above for autocycle cameras.With switch 309 in the iiare release panel 310 open, as shown in FIGURE17, the system is set for day operation.

Cameras used for both day and night operations usually have twoelectrically operated shutters arranged 180 out of phase with respect`to each other. That is, when one shutter is open the other is closedand as each pulse is applied to both shutters these conditions arereversed.

In day operation, the shutter pulses originate tat either of theswitches 304 and 305 in station computer unit 19 and the pulses are fedthrough the normally closed contacts of switch 311 in station relay box312 to a shutter control 313. The shutter control 313 is activatedduring day operation by closure of the operate switch 314 which connectsshutter control 313 to ground through the normally closed contacts ofswitch 315 in the station relay box. The closure of either switch 304 or305 by cam 174 results in the circuits of the shutter control 313applying a pulse to the closed camera shutter to open the latter and,after a predetermined period of time, applying another pulse to thecamera to close the second shutter and advance the film.

Conversion of the system shown in FIGURE 17 to night operation is madeby closing the ready switch 309 en the are release panel 310. Thiscauses a potential to be supplied from source 316 to one terminal of therelay coil 317 and to the Hash detector 318. Closure of the operateswitch 314 connects the other terminal of relay coil 317 to ground andthus energizes the relay coil. Relay coil 317, when energized, controlsthe switch blades of switches 311 and 315 to enable pulses from the`station computer to be transferred by switch 311 from the shuttercontrol 313 to the are ejector 319 through switch 309. The energizationof coil 274 also de-energizes the shutter control 313 and energizes acamera cir- 234 cuit which opens the closed shutter and transfers theinitiation of film re-cycle from the exposure control to the othercamera shutter.

Pulses caused by the closure of either switch 304 or 305 result in arelease of either a fiash cartridge or a flare bomb, depending uponwhich is provided, from the flare ejector 319. When the flare or bombexplodes, the flash is detected by the ash detector 318 and the lattercloses the open shutter of the camera and initiates re-cycle of thefilm. During this re-cyole, the shutter which was just opened is onceagain closed and the shutter which was just closed is ire-opened. At thecompletion of :re-cycle of the film and when it has resumed IMC speed,the closed shutter is opened to await the explosion of another flare.

Because of design factors inherent in the majority of IMC cameras, tomaintain the command signal within the camera designed parameter it isnecessary that only those push buttons on the station computer whichcorrespond to 60% overlap be depressed. This requirement is furthermodified when the camera is mounted in a remotely controlled rotatablemount of the type described hereinbelow. With the camera control systemshown in FIGURE 17, these requirements result in the need of two stationcomputers if overlapping other than 60% is desired. With a system ofthis type, one computer would provide the pulses for the camera shutterfor flares and the other computer would provide the IMC command signals.It will be appreciated by those skilled in the art that a system of thistype would be constructed in a manner similar to the system shown inFIGURE 16.

A pulse camera 43 in an IMC camera mount 42 is shown generally in FIGURE1 of the drawings and in greater detail in FIGURE 18 of the drawings. Aservo mo-tor 24 with power supplied by amplifier 25 and controlled by aDC. generator 23 together with the error signal ER drives a centralcomputer drive shaft 17 through gear changer 16 at a rotational speed of5.63 V/H revolutions per second, as has been previously describedhereinabove.

Coupled `to the yline shaft 17 as by the nn'ter gears shown are asynchro transmitter 18 and the station computer 29 of station computerunit 19. The rotor 320 of synchro transmitter 18 is thus driven at aspeed of 5.63 V/H. Also, it can be seen that rotor 320 receives powerfrom a transformer 321 in servo ampljer 44.

A synchro receiver 322 located in an IMC mount actuator 323 has itsstator windings 324 connected to the stator windings 32S of the synchnotransmitter 18 in the central computer 14. The rotor 325 of the synchroreceiver 322 is driven by a servo motor 327 through a gear box 328. Thegear box 328 has a fixed speed increase equal to the V/H constant andfor the example used throughout lthis specitication, the fixed speedincrease would be 5.6311. The synchro receiver 322 in connection withits associated servo amplifier 44 controls the speed of servo motor 327so that the latter rotates at a speed directly proportional to V/H. Itwill be appreciated that speed contr-ol is yachieved in the same manneras described hereinabove for an autocycle camera.

The servo motor 327 also drives a yone revolution clutch 329. A drivingdrum 330 is fixed to and rotates with the output shaft 331 of servomotor 327. A driven drum 332 is secured to a shaft 333 in any suitablemanner so as to be in axial alignment with driving drum 330. A spring334-, secured to drum 332, is tightly coiled around the driving anddriven drums 330 and 332, respectively, to operatively connect the drumsto the end that when drum 330 is turned by servo motor 327, drum 332 isalso turned.

A cam 335, shown as a round eccentrically mounted disc in both FIGURES18 and 19, is secured to shaft 33 and rotates with it. It will beappreciated that the illustration of a round cam 33S is illustrativeonly of the fact that the uniform angular velocity of a shaft such asshaft 333 is converted to a rocking motion at the camera and

1. A CONTROL SYSTEM FOR PROVIDING IMAGE MOTION COMPENSATION IN AN AERIALCAMERA MOUNT COMPRISING A ROTATABLE SHAFT, VELOCITY SERVO MOTOR MEANSFOR CAUSING SAID SHAFT TO ROTATE AT A SPEED CORRESPONDING TO THEAIRCRAFT VELOCITY TO ALTITUDE RATIO, SYNCHRO TRANSMITTER MEANS COUPLEDTO SAID ROTATABLE SHAFT FOR TRANSMITTING ELECTRICAL SIGNALS INACCORDANCE WITH THE SHAFT ROTATION, ACTUATING MEANS COUPLED TO THECAMERA MOUNT FOR ROCKING THE MOUNT, SAID ACTUATING MEANS COMPRISINGSYNCHRO RECEIVING MEANS CONNECTED TO SAID SYNCHRO TRANSMITTING MEANS, ASERVO MOTOR,